1. Field of the Invention
The invention relates to a nickel-based alloy.
2. Description of the Related Art
Nickel-based alloys are used, among other things, for producing electrodes of ignition elements for internal combustion engines. These electrodes are exposed to temperatures between 400° C. and 950° C. In addition, the atmosphere alternates between reducing and oxidizing conditions. This produces material destruction or a material loss caused by high-temperature corrosion in the surface region of the electrodes. The production of the ignition spark leads to further stress (spark erosion). Temperatures of several 1000° C. occur at the foot point of the ignition spark, and in the event of a break-through, currents of up to 100 A flow during the first nanoseconds. At every spark-over, a limited material volume in the electrodes is melted and partly evaporated, and this produces a material loss.
In addition, vibrations of the engine increase the mechanical stresses.
An electrode material should have the following properties:                good resistance to high-temperature corrosion, particularly oxidation, but also sulfidation, carburization, and nitration;        resistance to the erosion that occurs as the result of the ignition spark;        the material should not be sensitive to thermal shocks and should be heat-resistant;        the material should have good heat conductivity, good electrical conductivity, and a sufficiently high melting point;        the material should be easy to process and inexpensive.        
Nickel alloys, in particular, have a good potential for fulfilling this spectrum of properties. They are inexpensive in comparison with precious metals, they do not demonstrate any phase conversions up to the melting point, like cobalt or iron, they are comparatively non-sensitive to carburization and nitration, they have good heat resistance and good corrosion resistance, and they can be deformed well and welded.
Wear caused by high-temperature corrosion can be determined by means of mass change measurements as well as by means of metallographic studies after aging at predetermined test temperatures.
For both damage mechanisms, high-temperature corrosion and spark erosion, the type of oxide layer formation is of particular significance.
In order to achieve an optimal oxide layer formation for the concrete application case, various alloy elements are known in the case of nickel-based alloys.
In the following, all the concentration information is given in % by mass unless explicitly noted otherwise.
From DE 29 36 312, a nickel alloy has become known, consisting of about 0.2 to 3% Si, about 0.5% or less Mn, at least two metals, selected from the group consisting of about 0.2 to 3% Cr, about 0.2 to 3% Al, and about 0.01 to 1% Y, remainder nickel.
In DE-A 102 24 891 A1, an alloy on the basis of nickel is proposed, which has 1.8 to 2.2% silicon, 0.05 to 0.1% yttrium and/or hafnium and/or zirconium, 2 to 2.4% aluminum, remainder nickel. Such alloys can be worked only under difficult conditions, with regard to the high aluminum and silicon contents, and are therefore not very suitable for technical large-scale use.
In EP 1 867 739 A1, an alloy on the basis of nickel is proposed, which contains 1.5 to 2.5% silicon, 1.5 to 3% aluminum, 0 to 0.5% manganese, 0.5 to 0.2% titanium in combination with 0.1 to 0.3% zirconium, whereby the zirconium can be replaced, in whole or in part, by double the mass of hafnium.
In DE 10 2006 035 111 A1, an alloy on the basis of nickel is proposed, which contains 1.2 to 2.0% aluminum, 1.2 to 1.8% silicon, 0.001 to 0.1% carbon, 0.001 to 0.1% sulfur, maximally 0.1% chromium, maximally 0.01% manganese, maximally 0.1% Cu, maximally 0.2% iron, 0.005 to 0.06% magnesium, maximally 0.005% lead, 0.05 to 0.15% Y, and 0.05 to 0.10% hafnium or lanthanum or 0.05 to 0.10% hafnium and lanthanum, in each instance, remainder nickel, and production-related contaminants.
In the brochure “Drähte von ThyssenKrupp VDM Automobilindustrie” Publication N 581, Jan. 2006 Edition, on page 18, an alloy according to the state of the art is described, NiCr2MnSi with 1.4 to 1.8% Cr, max. 0.3% Fe, max. 0.5% C, 1.3 to 1.8% Mn, 0.4 to 0.65% Si, max. 0.15% Cu, and max. 0.15% Ti. As an example, a batch T1 of this alloy is indicated in Table 1. Furthermore, in Table 1, the batch T2 is indicated, which was melted according to DE 2936312 with 1% Si, 1% Al, and 0.17% Y. An oxidation test at 900° C. in air was conducted on these alloys, whereby the test was interrupted every 96 hours and the mass change in the samples caused by oxidation was determined (net mass change). FIG. 1 shows that T1 has a negative mass change from the start. In other words, parts of the oxide that formed during oxidation have flaked off from the sample, so that the mass loss caused by flaking of oxide is greater than the mass increase caused by oxidation. This is disadvantageous, because the protective layer formation at the flaked-off locations must always begin anew. The behavior of T2 is more advantageous. There, the mass increase caused by oxidation predominates during the first 192 hours. Only afterwards is the mass increase caused by flaking greater than the mass increase caused by oxidation, whereby the mass loss of T2 is clearly less than that of T1. In other words, a nickel alloy with approx. 1% Si, approx. 1% Al, and 0.17% Y demonstrates clearly more advantageous behavior than a nickel alloy with 1.6% Cr, 1.5% Mn, and 0.5% Si.